Electric control system for an electrically adjustable conveying plant



March 10, 1970 ELECTRIC CONTROL SYSTEM FOR AN ELECTRICALLY Filed April 14, 1967 J. MARCHER ADJUSTABLE CONVEYING PLANT 2 Sheets-Sheet 1 Inn '11 um Im 4 m MI. 7 z

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ELECTRIC CONTROL SYSTEM FOR AN ELECTRICALLY ADJUSTABLE CONVEYING PLANT Filed April 14, 1967 2 Sheets-Sheet 2 ii; U

BALANCE AMPL/F/Er? F p 5 4 Q AMPL/- AMPLZ- g F/ER F/ER m 1% Q 8ALA/VCE AMPLIFIER L V mv NToR JR6EN MARCHE-R 1: 64m, 5 a wwla United States Patent 3,500,134 ELECTRIC CONTROL SYSTEM FOR AN ELEC- TRICALLY ADJUSTABLE CONVEYING PLANT Jorgen Marcher, Bagsvaerd, Denmark, assignor to H. Nielsen & Son, Maskinfabrik A/S, Marielundvej, Denmark Filed Apr. 14, 1967, Ser. No. 631,070 Claims priority, application Denmark, Apr. 15, 1966, 1,956/ 66 Int. Cl. H01h 47/36; G01r 33/12; G08b 13/00 US. Cl. 317153 7 Claims ABSTRACT OF THE DISCLOSURE Two coaxial, coreless, and non-inductively associated coil pairs, each having inductively coupled primary and secondary windings, are disposed adjacent to a predetermined point in a conveyor path. One of the coil pairs (a sensor coil pair) is closer to the conveyor path than the other coil pair (a reference coil pair). The coil pairs form legs in a bridge circuit which is balanced where there is no magnetically energizable body at the predetermined point of the conveyor path. The presence of such a body near the sensor coil pair causes the bridge circuit to become unbalanced and initiates a change in the movement of the body on the conveyor.

The invention relates to an electric control system for an electrically adjustable conveying plant, which is adapted to give off an input voltage to an indicator member at the presence of a preferably energizable metal body at a predetermined point of the conveyor path, the said indicator member controlling a change in the direction of movement of the body along the conveying path.

Plants of the aforesaid kind are known, but it is difficult with the available plants to obtain the necessary reliability in operation, more particularly when the conveyor is to convey energizable or electrically conducing bodies of heavy weight and bulk such as steel sheets or plates and objects made of electrically conducing materials, in which defects may give rise to heavy trouble and damage of the conveyors and the objects conveyed alike.

It is the object of the invention to devise an electric control system of the aforesaid kind possessing great operational realiability, since it is constructed of stable and robust components and is sufficiently sensitive to the presence of energizable or electrically conducting metal bodies without being oversensitive to any magnetic stray fields from surrounding electromagnetic devices and machines and their supply wires.

An essential feature of an electric control system according to the invention is an alternating current bridge one arm of which is constituted by a primary and a secondary coreless coil, the said coils being so arranged coaxially in relation to and close to each other as to form an inductively coupled first coilpair, termed the sensor coil pair, which is disposed close to the predetermined point of the conveyor path, while the other adjacent arm of the bridge is constituted by a primary and a secondary r' 3,500,134 Ice Patented Mar. 10, 1970 axial distance apart that there is no appreciable inductive coupling between the two coil pairs, whilst the third and fourth arms of the bridge are constituted each by its variable resistance element such as a potentiometer the tap of which is connected to one input terminal of the indicator member, whereas its other input terminal is connected to a common point between the sensor coil pair and the reference coil pair.

The result obtained is that on adjustment of the tap of the potentiometer, balance in the bridge is obtainable when the sensor coil pair and the reference coil pair have identical electric qualities as aimed at, and as long as there is no energizable or conducting body near the predetermined point of the conveying path, whereas an error voltage will arise in the bridge and the indicator member be acted upon when an energizable or conducting body on its Way along the conveying path gets into the vicinity of the sensor coil pair, by which the electric qualities of the latter, such as its self-induction, its effective resistance and the mutual induction between its primary and secondary windings are altered. The error voltage produced is thus a criterion indicating that an energizable or conducting body is present in the vicinity of the predetermined point of the conveying path, and the error voltage detected by the indicator member may therefore, after any necessary amplification, be used to control the change of the direction of movement of the body along the conveing path or for stopping or starting the movement or for shunting to a side track of the conveying path. A further result obtained is that the sensor coil pair and the reference coil pair owing to their coaxial location in relation to each other are subjected to substantially uniform action of any magnetic stray fields that may be present from electrical machines and devices located near the conveying path and from their supply cables so that the said stray fields will have no appreciable influence upon the sensitivity of the control apparatus.

In a suitable embodiment of the plant according to the invention both the sensor coil and the reference coil pair have the identical number of windings, the identical wire thickness and the identical outer dimensions and are made of identical materials, as a result of which any temperature variations in the surroundings of the coils have no appreciable influence upon the balance of the bridge or the amount of the error voltage produced by the presence of the energizable body.

In a preferred embodiment of the plant according to the invention the primary winding of the sensor coil pair is disposed close to and parallel with the path of movement of the energizable body, and secondary winding of the reference coil pair is disposed remote from the said path of movement, whereas the secondary winding of the sensor coil pair and the primary winding of the reference coil pair are disposed close to the first-mentioned and the last-mentioned winding, respectively, and on such side of these as is remote from the path of movement.

The result obtained is that the primary winding of the sensor coil pair produces, when the energizable or conducting body is present, a relatively powerful magnetic field through the body and the secondary winding of the sensor coil pair, while the secondary winding of the reference coil pair, which is disposed remote from the energizable or conducting body, is not appreciably influenced by the presence of the body and therefore substantially preserves its electric constants.

The indicator member may in a suitable embodiment according to the invention further consist of two balanced phase-sensitive amplifiers the input terminals of which are connected in parallel and coupled to the output of the first amplifier, one of the phase-sensitive amplifiers being adapted to give off a negative output direct voltage which is maximum when the input signal to the two balanced phase-sensitive amplifiers is displaced by 90 in relation to the supply voltage to the primary windings of the alternating current bridge, whereas the other phasesensitive amplifier is adapted to give off a positive output voltage which is maximum when the input voltage is likewise 90 displaced in relation to the said supply voltage, and the said two output voltages are each connected to its separate outer point of two series-connected resistors of equal value, the common point of which is connected, preferably through an amplifier, to an electromagnetic control member for changing the direction of movement of the energizable or electrically conducting body along the conveying path.

The result obtained is that the electromagnetic control member receives no current from the common point when the input signal is displaced by 90 in relation to the said supply voltage, which will be the case when the bridge is in balance or very nearly in balance. If, however, the unbalance exceeds a predetermined value of the input signal, the control member will be activated and perform a predetermined change of direction of movement of the energizable or conducting body such as start or stop of its movement or change the points of a siding of the conveying path. Simultaneously an acoustic or optical signal device connected in parallel with the control member may enter into operation to indicate that the said change has taken place.

The invention will now be described in detail with reference to the drawings, in which FIGURE 1 is a wiring diagram of an electric control system according to the invention,

FIGURE 2 is a diagrammatical representation of an embodiment of same and with a sensor coil pair, a reference coil pair and an indicator member and with an energizable or electrically conducting body disposed close to the sensor coil pair,

FIGURE 3 shows an embodiment of a sensor unit for control systems according to the invention, viewed in section on the line III-III of FIGURE 4,

FIGURE 4 is a section of same on the line IVIV of FIGURE 3,

FIGURE 5 is a section of same taken on the line VV of FIGURE 3, and

FIGURE 6 is a key diagram of another embodiment of the indicator member of the control system according to the invention.

FIGURE 1 shows an alternating current bridge for an electrically adjustable conveying plant with a conveying path which is defined in part by a roller W which is driven by a motor Y, the said alternating current bridge being fed with current from an alternating current generator G. One arm of the said bridge is constituted by a coreless primary and secondary wire coil, A and C, respectively, disposed coaxially and close to each other so as to form an inductive first coil pair AC coupled through a mutual induction M; and termed the sensor coil pair, the said coil pair being disposed close to a predetermined point of the conveying path through which an energizable or electrically conducting body F as indicated in FIGURE 2 moves across the coil pair AC, by which the mutual induction M and the self-induction L of the secondary coil C are varied. In addition, the effective resistance R in which is included the effective resistance originating from the coil A is varied. The other arm of the bridge adjacent to the first arm is likewise constituted by a coreless primary and secondary wire coil, B and D, respectively, likewise disposed coaxially in relation to and close to each other in such manner as to constitute an inductive, second coil pair B, D, connected through a mutual induction M and termed the reference coil pair. The winding D has an effective resistance R in which is included the effective resistance originating from the winding B and a self-induction L The two coil pairs A, C and B, D are disposed coaxially in relation to each other, but at a substantial distance apart as indicated in FIG- URES 2, 3 and 4 so that there is no appreciable inductive coupling between the two coil pairs. The third and fourth arms of the bridge are constituted each by its variable resistance element, R and R respectively, which may be composed as a potentiometer P with an adjustable tap H which is connected to one input terminal of an indicating member F such as an alternating current amplifier, to the output terminals of which there is connected a control relay Q, for example through a rectifier E. The contact N of the control relay Q is connected with means for changing the direction of movement of the energizable body along the conveying path, for example for stopping and starting the movement produced by motor Y or for switching a side track of the conveying path. The other input terminal of the indicator member F is connected to a common point 0 bet-ween the sensor coil pair A, C and the reference coil pair B, D. The two coil pairs have identical electric qualities as aimed at, that is, R =R L =L and M M as long as there is no energizable or conducting body opposite the sensor coil pair, and the bridge may therefore be balanced when the tap H of the potentiometer P is adjusted in such manner that R =R In the two coil pairs there are fiows of current 1' and i which, in that case, are equal, and in the input impedance of the amplifier, which may be reckoned to be approximately purely ohmic, that is, equal to a resistance R there is a current flow i O. If an energizable body L is located opposite the coil pair A, C, R R L L and M M by which there is produced an input voltage e =i R across the input of the amplifier, and a direct current is produced through the rectifier E and the relay Q, which will then attract and indicate the presence of the body L by closing the contact N to the means which change the direction of movement of th body L, for example stopping or starting the movement or switching a side track in the conveying path.

A simple calculation shows that when R =R =R =R is substantially smaller than iw(L +M,)/ 2, which conditions may readily be satisfied, when e =i that is, the input voltage is proportional with the current i and with the sum of the differences between the inductive and mutual inductions of the two bridge arms or alternatively between the effective resistances R and R that is, the bridge will be highly sensitive to the presence of energizable bodies, just as it will also be sensitive to non-magnetizable electrically conducting bodies which will produce a short circuiting effect, both on the self-induction L and on the mutual induction M; and increase the effective resistance R; in relation to R In order to obtain maximum sensitivity of the bridge, it is suitable according to the invention that both the sensor coil pair A, C and the reference coil pair B, D have the identical number of windings, the identical wire thickness and identical outer dimensions and that they are made of identical materials, by which the error voltage is almost equal to zero when there is no energizable or electrically conducting -body in the vicinity of the sensor coil pair.

In a preferred embodiment of the sensor unit the primary winding A of the sensor coil pair A, C is as shown in FIGURES 2, 3 and 4 disposed close to and parallel with the path of movement of the energizable or electrically conducting body, and the secondary winding B of the reference coil pair B, D is disposed remote from the said path of movement, Whereas the winding C of the Sensor coil pair and the primary winding D of the reference coil pair are disposed close to the firstmentioned winding, and the lastmentioned winding, respectively, and on such side of these as is remote from the path of movement. This will ensure that the winding C is acted upon by a relatively powerful magnetic field produced by the winding A, which is indicated by stippled lines of force in FIGURE 2, and the said winding C is therefore also intensely influenced by variations in the said magnetic field, caused by the presence of an energizable or electrically conducted body L. In contrast, the winding D is located remote from the energizable or conducting body L, and the said winding is therefore not appreciably acted upon by the presence of such bodies in the conveying path.

In practice, the two coil pairs A, C, and B, D are built together as a sensor unit which, as shown in FIGURES 3, 4 and 5 is enclosed by a casing Z of a non-metallic material such as plastic, the said casing being at its open underside attached to a permanent metallic support J which, in view' of the magnetic symmetry of the coil pairs, is provided with a suitable recess U. The two opposed sides of the sensor unit may be provided with conductor partitions T for protecting the unit against mechanical darriage. The casing Z may after the coil pairs A, C and B, D having been arranged be filled with a casting of electrically insulating material, partly to stabilize the unit mechanically, partly to ensure a uniform temperature in same.

In one embodiment of the plant according to the invention the indicator member consists as shown in FIG- URE 6, besides of the alternating current amplifier F of two balanced phase-sensitive amplifiers F and F the input terminals of which are connected in parallel and coupled direct to the output of the amplifier F One amplifier F feeds to a load resistance R a negative direct current of a value dependent on the phase of the input signal so that the output voltage is maximum when the input voltage to the amplifier F is displaced by 90 in relation to the supply voltage to the sensor unit. The other amplifier F feeds to a load resistance R a positive direct current the value of which is at its maximum when the input voltage is likewise displaced by 90 in relation to the supply voltage to the sensor unit. When the input voltage is displaced by 90 in relation to the said supply voltage as is the case when the bridge is in balance the two balanced amplifiers F and F will give off equal direct voltages but with reversed signs in the common point of the resistances R and R and a direct current voltmeter V which is connected to the common point will indicate the voltage zero, just as a direct current amplifier E; which is connected with its input to the common point will not give any signal voltage across its output to a relay Q that is connected to same lamp indicators X. If the error signal across the amplifier F however, exceeds a predetermined value, the output voltage of the amplifier F or of the amplifier F will be increased, and there will be a resultant voltage at the common point between the resistances R and R sufiicient to securely act upon the relay Q and to light the indicators X to show that the presence of an energizable or electrically conducting body has activated the control system.

What is claimed is:

1. An electric control system for an electrically adjustable conveying plant, which is adapted to give off an input voltage to an indicator member at the presence of 9. preferably energizable metal body at a predetermined point of the conveyor path, the said indicator member controlling a change in the movement of the body along the conveying path, characterized by an alternating current bridge one arm of which is constituted by a primary and a secondary coreless coil, the said coils being arranged coaxially in relation to and close to each other as to form an inductively coupled first coil pair, termed the sensor coil pair, which is disposed close to the predetermined point of the conveyor path, while the other adjacent arm of the bridge is constituted by a primary and a secondary coreless coil spaced further than the sensor coil pair from the predetermined point of the conveyor path, the said coils being likewise arranged coaxially with and ,close to each other so as to constitute an inductively coupled second coil pair, termed the reference coil pair, the sensor coil pair and the reference coil pair being coaxial and spaced axially at a location where they are exposed to substantially uniform action of stray magnetic fields; but at a substantial axial distance apart that there is no appreciable inductive coupling between the two coil pairs, whilst the third and fourth arms of the bridge are constituted each by its variable resistance element such as a potentiometer the tap of which is connected to one input terminal of the indicator member, whereas its other input terminal is connected to a common point between the sensor coil pair and the reference coil pair.

2. An electric control system as claimed in claim 1, characterized in that both the sensor coil pair and the reference coil pair have the identical number of windings, the identical wire thickness and the identical outer dimensions and are made of identical materials.

3. An electric control system as claimed in claim 2, characterized in that the primary winding of the sensor coil pair is disposed close to and parallel with the path of movement of the energizable body and the secondary winding of the reference coil pair is disposed remote from the said path of movement whereas the secondary winding of the sensor coil pair and the primary winding of the reference coil pair are disposed close to the firstmentioned and the lastmentioned winding, respectively, and on such side of these as is remote from the path of movement.

4. An electric control system as claimed in claim 3, characterized in that the system includes an electromagnetic control member and the indicator member consists of a first amplifier and two balanced phase-sensitive amplifiers the input terminals of which are connected in parallel and coupled to the output of the first amplifier, one of the phase-sensitive amplifiers being adapted to give off a negative output direct voltage which is maximum when the input signal to the two balanced phasesensitive amplifiers is displaced by in relation to the supply voltage to the primary windings of the alternating current bridge, whereas the other phase-sensitive amplifier is adapted to give oif a positive output voltage which is maximum when the input voltage is likewise displaced by 90 in relation to the said supply voltage, the said two output voltages being each connected to its separate outer point of two series-connected resistors of equal value, the common point of which is connected to the electromagnetic control member for changing the direction of movement of the energizable or electrically conducting body along the conveying path.

5. An electric control system as claimed in claim 1, characterized in that the primary winding of the sensor coil pair is disposed close to and parallel with the path of movement of the energizable body and the secondary winding of the reference coil pair is disposed remote from the said path of movement, whereas the secondary winding of the sensor coil pair and the primary winding of the referencecoil pair are disposed close to the firstmentioned and the lastmentioned winding, respectively, and on such side of these as is remote from the path of movement.

6. An electric control system as claimed in claim 1, characterized in that the system includes an electromagnetic control member and the indicator member consists of a first amplifier and two balanced phase-sensitive amplifiers the input terminals of which are connected in parallel and coupled to the output of the first amplifier, one of the phase-sensitive amplifiers being adapted to give off a negative output direct voltage which is maximum when the input signal to the two balanced phase-sensitive amplifiers is displaced by 90 in relation to the supply voltage to the primary windings of the alternating current bridge, whereas the other phase-sensitive amplifier is adapted to give olf a positive output voltage which is maximum when the input voltage is likewise displaced by 90 in relation to the said supply voltage, the said two output voltages being each connected to its separate outer point of two series-connected resistors of equal value, the common point of which is connected to the electromagnetic control member for changing the direction of movement of the energizable or electrically conducting body along the conveying path.

7. An electric control system as claimed in claim 6, characterized in that the primary winding of the sensor coil pair is disposed close to and parallel with the path of movement of the energizable body and the secondary winding of the reference coil pair is disposed remote from the said path of movement, Whereas the secondary winding of the sensor coil pair and the primary winding of thereference coil pair are disposed close to the firstmentioned and the lastmentioned windings, respectively, and on such side of these as is remote from the path of movement.

References Cited UNITED STATES PATENTS LEE T. HIX, Primary Examiner CHARLES L. YATES, Assistant Examiner US. Cl. X.R. 

